In a conventional air-conditioning apparatus, cylindrical tubes mainly made of copper form a refrigerant circuit to circulate refrigerant between an outdoor unit and an indoor unit. Typically in this refrigerant circuit, passes are extremely long and are branched or joined complicatedly. For this reason, the copper pipes are, by brazing, often bonded together at each point of the refrigerant circuit. The point where two pipes are bonded together is often manually brazed using a hand burner by a worker. However, for the point where portions to be brazed are closely spaced, automatic brazing may be performed using an automatic brazing device. Examples of using automatic brazing include the case where many pipes are brazed to pipes of a heat exchanger.
At various portions to be brazed as described above, typically, one end of one pipe is inserted into one end of another pipe, a brazing material is supplied to portions in which both the pipes overlap with each other and then brazing is performed. In the most common method for such brazing, both original pipes have the same outer diameter, and a tip end of one of the pipes is expanded or narrowed. Subsequently, one of the pipes is inserted into the other pipe so that a slight clearance is left between one of the pipes and the expanded or narrowed tip end of the other pipe. Alternatively, both original pipes may have different outer diameters, and thus one of the pipes may be inserted into the other pipe by using a slight clearance between both original pipes without expanding or narrowing of the pipe. Also, one of the pipes may be expanded and another pipe may be narrowed, and then the narrowed pipe may be inserted into the expanded pipe.
To braze such pipes, various measures are taken depending on circumstances. The slight clearance is left between the pipes at a portion at which one of the pipes is inserted into the other one of the pipes as described above, and a molten brazing material is poured into the portion while the portion is being heated. Subsequently, heating is terminated to complete bonding by solidifying the brazing material. However, although an ideal clearance varies depending on the material and dimensions of pipes to be brazed and the type of a brazing material to be used, a typical clearance for pipes used for an air-conditioning apparatus is often between 0.1 mm and 0.2 mm. Further, the dimensions of the clearance need to be uniform across an entire circumference while one of the pipes is not obliquely inserted into the other one of the pipes.
As described above, the dimensions of the clearance between the pipes need to be constantly uniform across the entire circumference regardless of the type of an insertion process. In this case, at least one of the pipes targeted for insertion is provided with about three protrusions each having the same height as the dimension of the clearance, and the protrusions are provided in the circumferential direction of the pipe. With this configuration, a design has been proposed to match the axial centers of the pipes targeted for insertion (see Patent Literature 1, for example).